Such heat exchangers are used especially in motor vehicles having internal combustion engines, so as to act either as a cooling radiator for the engine, or as a heating radiator for the cabin of the vehicle. In either of these two applications, the tubes in the tube bundle constituting the plurality of sets of tubes carry a fluid, which is generally a mixture of water and anti-freeze, which passes through the tubes that form part of the engine cooling circuit, while a stream of air is directed over the tubes in the bundle. It is common practice to provide, in known heat exchangers of this type, the same number of holes in the header plate as there are tubes in the bundle, so that each tube end portion will be received individually ;n a respective individual hole in the header plate, to which it is sealingly secured.
In the specification of French patent application No. 91 03411 of the present Applicants, there is disclosed a heat exchanger of the type comprising a bundle of parallel tubes arranged in sets, together with a header plate which is formed with holes, in which each said hole receives the respective end portions of a plurality of adjacent tubes of different sets of tubes in the bundle, with a compressible sealing gasket being interposed between the edge of the hole and the end portions of the tubes.
Due to the fact that the respective end portions of a plurality of tubes are received in a single hole in the header plate, instead of each end portion being received individually in one hole in &he latter, the pitch defined between the axes of the tubes, as between one set of tubes and the other, is able to be set at a minimum value. In this way, the performance of the heat exchanger can be optimised, with minimal width of the header plate.
However, in the last mentioned type of heat exchanger of the prior art, the shape of the holes is such that, after assembly, the sealing gasket cannot be compressed uniformly over the whole periphery of the tubes which are introduced into any one of the holes in the header plate. This compression is in fact weaker in that region of the gasket which lies between two adjacent tube end portions, since this region of the gasket is thinner than elsewhere on the gasket. The result is that poor sealing can occur, which is prejudicial to proper operation of the heat exchanger.